Coagulation is the initial make-or-break unit process in water-pollutant separation systems. Flocculation immediately follows coagulation. Combined, coagulation-flocculation represents pretreatment processing for the formation of floc (˜mm size aggregates that incorporate pollutants) for their subsequent physical separation. Separation of floc-pollutants is accomplished by a spectrum of large-scale separation process applications spanning from drinking water filtration (granular-media) to membranes and desalting pretreatment, to wastewater treatment, fats-oil-grease removal from industrial wastewater, waste metal and trace element removal, to dewatering including paper making and sludge dewatering.
Coagulation involves chemical addition and dispersion to water that is to be treated. Coagulation is remarkably powerful. It can induce 10,000-fold pollutant-particle size changes, and >1,000,000-fold reduction in number concentration of infectious organisms such as the amoeba Cryptosporidium. Coagulation is also versatile as it may induce removal of a diverse variety of pollutant species including;                (i) Ions of arsenic, phosphorus, fluorine, and trace metals;        (ii) Dissolved organics that may form carcinogens;        (iii) Algae, dead microorganisms, their cellular detritus, and infectious virus, bacteria, amoeba;        (iv) Particulate matter harboring other pollutants.        
However, the successful application of coagulation represents a challenge because coagulation-flocculation effects are manifold, slow to manifest, varied, and are used in a wide range of applications. Most importantly, coagulation-flocculation pretreatment represents the ‘big lever’ for the plant operators for controlling pollutant-removal performance both quality and quantity (throughput) wise.
Coagulation is instantaneous whereas flocculation nominally requires ˜½ hour to several hours in older facilities for dilute suspensions, but only minutes for dense slurries. Nominally, coagulation converts otherwise stable negatively charged pollutant species into neutral ‘sticky’ bodies that gradually grow in size as a result of particle-particle collisions caused by mild turbulent fluid mixing. A fundamental requirement of coagulant dosing is that the total negative charged demand of water must be met by the positive-charge supplied by the coagulant chemicals, referred to as charge neutral coagulation. Dosing beyond this point may be more costly or counterproductive. Flocculation results in the aggregation of pollutant-coagulant sub-particles into larger and larger, more easily removable, entities, or floc particles that ultimately reach some steady-state size. That size depends upon the nature of the mixing regime and floc strength characteristics for a given raw water quality and coagulation chemistry. Mixing intensity control represents the physical means for the plant operators to manipulate floc particle characteristics, for a given coagulation-chemistry regime.
Because the terms coagulation and flocculation are used interchangeably by some, these and related terms require defining as to their meaning as used in this invention disclosure. Coagulation refers to the action of the addition of chemical species that in turn lead to the instantaneous precipitation, adsorption, and destabilization of dissolved and particulate matter. Flocculation refers to the agglomeration or aggregation of the destabilized colloids and precipitates. Coagulation-flocculation refers to the coupled unit processes as a pretreatment system preceding the pollutant-floc separation step(s). The term operationally controllable variables—of coagulation-flocculation processing—refer nominally to coagulant chemical dosing and to flocculation mixing intensity.